The unevenness of yarn is one of the most important parameters of yarn quality control in the spinning mill. This quality control has until now been carried out almost exclusively in the laboratory on the basis of random samples. However, the procedures now in general use are not well suited to prompt identification of so-called mavericks, i.e. places in which the yarn deviates significantly from the desired diameter. Such mavericks are a frequent occurrence and can only be detected if all the production stations are subject to a control. However a comprehensive quality control directly at each production station is absolutely unrealistic.
It is now usual to use so-called traveling sensors to detect the number of thread breakages at each spinning station. While, the number of thread breakages at the individual spinning stations gives an indication of possible mavericks, the detection of breakage events alone does not adequately address the problem.
A device for monitoring a consecutive series of work stations of a textile machine for thread breakage is known in particular from U.S. Pat. No. 4,122,657. In this system, a scanning head is guided past the work stations on a guide bar for contactless recording of electrical signals. This traveling sensor or scanning head reacts according to a magnetic principle to the rotation of the ferromagnetic traveler of the ring spinning machine work station. This gives rise to a disadvantage. Since the sensor responds to stoppage of the traveler and this only occurs when the ballooning thread, as a result of a break, no longer propels the traveler around the ring, the system determines only thread breakage. In particular, it delivers no information on the quality of the spun yarn, for it does not react to the yarn as such.
For practical reasons quality control in the laboratory does not take place until several days after the random samples have been taken. The possibility of a prompt reaction to any changes of a general type is therefore limited.